This application is a 371 of PCT/IT97/00187 filed Jul. 26, 1997.
The present invention concerns bioadhesive complexes of polycarbophil and azole antifungal or antiprotozoal drugs. More specifically, the invention relates to the formulation of a complex of a cross-linked polyacrylic acid having remarkable mucoadhesive properties, known with the name of polycarbophil, and an imidazole or triazole derivative having antifungal or antiprotozoal activity, in the base form, for use in the topical treatment of mucosal affections.
As it is known, the diseases of a microbial origin affecting the mucous membranes, which may be treated by exploiting the trans-mucosal administration route, are many and widespread. In particular, among the diseases of this kind which affect the urogenital system, the mycotic infections are very common, and among these, specifically, the candidiases.
Candida albicans represents the species belonging to the Candida genus which is most commonly involved in human candidiases, and is the only species pathogenic on laboratory animals. The said species is held to be responsible of most superficial mycoses (muco-cutaneous mycoses) and of some serious deep mycoses, and is commonly present on the mucous membranes surfaces, such as those of the buccal cavity and of the gastrointestinal tract in man, in equilibrium with the endemic flora of the said regions. In the healthy population equilibrium conditions are normally established between the invasive potential of the fungus and the defence mechanisms of the host, which are able to limit the tissue invasion and, possibly, to eradicate the infection from the mucous membranes surface. The onset of a pathological process is the consequence of the breach of such equilibrium, and this may be either due to the different virulence of the infecting yeast or to the reduced resistance of the host. The importance of the host defence mechanisms, both natural and acquired, against candidiases is strongly confirmed by the incidence of fungal infections, and, specifically, candidiases, in immunocompromised subjects.
The candidiases of the urogenital system, much more widespread in women than in men, are characterised by itch and discharge and, upon clinical examination, by erythema, edema and, sometimes, ulcerous or papular lesions. Epidemiologic statistics on the incidence of vaginal candidiases are difficult to establish, although it may be considered that the said incidence has greatly increased in the last few years, also due to a wider use of hormone contraceptives and of antibiotic antimicrobials. Candidiases, and in general all of the fungal affections of the urogenital system, may be therapeutically treated with antimicrobial drugs for topical use, specifically imidazole derivatives such as econazole, tioconazole, miconazole and the like, or triazole derivatives such as terconazole, or also with drugs for oral administration, in particular of the triazole type, such as fluconazole. It is usually recommended to initially use the topical azole therapy, to be replaced by a systemic therapy in non responsive patients or in patients who do not withstand the topical therapy. This is due to the slight toxicity of the agents for systemic administration in comparison with agents which perform their activity in situ, as well as to the need to limit the use of these drugs in order to avoid the occurrence of resistant strains.
Among the antifungal drugs mentioned above, econazole, i.e. 1-{2-[(4-chlorophenyl)methoxy]-2-(2,4-dichlorophenyl)ethyl}-1H-imidazole, is particularly widespread and extensively tested. It has been synthesised by Godefroi et al. in 1969 (J. Med. Chem., 12, 1969, 784, and U.S. Pat. No. 3,717,655). The antimicrobial activity of econazole, which has been extensively shown in vitro, is exerted against a wide variety of fungi and against some gram-positive bacteria, while no activity on gram-negative bacteria is present. The main site of the antimicrobial action is represented by the cellular membrane system, similarly to what happens for the other imidazole antifungal agents. In vitro tests with Trichophyton rubrum, Saccharomyces cerevisiae, and Candida albicans have shown an increase in the permeability of the cell covering exposed to econazole. Said increase occurs both in the growing and in the grown-up cells, thus showing that the antimicrobial activity is due to an action on the formed membranes, and not to the formation of defective membranes in the growth phase. The main action of the drug is the inhibition of 14-xcex1-demethylase, a cytochrome P450-dependent microsomial enzyme system important for the synthesis of sterols. The said action has two effects: it causes a build-up of 14-xcex1-methylsterols, and compromises the synthesis of ergosterol, which is necessary to the cytoplasm membrane. The built-up methylsterols may desegregate the close packing of the phospholipids acyl chains, thus compromising the functions of some enzyme systems connected to the membrane.
Econazole is used mainly for topical administration in the treatment of vaginal dermatomycoses and candidiases. Several medicinal products containing econazole as the active ingredient are present on the market, specially for vaginal administration. In most of the said medicinal products econazole is not present as the base, but in the form of its nitrate salt.
Another kind of microbial diseases which have been treated with therapies based on azole active ingredients, to be administered normally through the trans-mucosal route, are the infections caused by protozoa of the genus Tnchomonas. These infections generally occur in women, as cervicites, vaginites and vulvovaginites, which may also be associated with candidiases or with other bacterial infections. The active ingredient of choice for trichomoniases is metronidazole, which also belongs to the group of imidazole derivatives. For the topical treatment of infections caused by Trichomonas, both in the man and in the woman, metronidazole is advantageously combined with an imidazole derivative having mainly an antifungal action, i.e. clotrimazole.
The conventional administration forms used for the topical antimicrobials of the kinds referred to above are most commonly creams, suppositories for vaginal administration (pessaries, inserts, ovules) and tablets. In the case of econazole, for instance, there are commercially available pessaries and creams based on econazole nitrate, which represent the preparations of choice, as well as douches (lavages) and foams for external use, both in the nitrate and in the base form, which are generally used as adjuvants in the therapy. Pessaries (containing from 50 to 150 mg of active ingredient) and creams (with 1% by weight of active ingredient, to be applied in 5 g doses) are administered once a day, preferably just before going to bed in order to improve retention. The said forms do not allow, in general, to obtain an optimal bioavailability of the drug. Actually, for the therapy to perform at best its action it is necessary that the following conditions are realised: a) a good adhesion of the medicament on the infected site, and b) the complete release of the active ingredient. Very often the above does not occur with the medicinal products now in use: in the case of the suppositories for vaginal administration, in particular, the problem of retention arises, since as soon as the fusion has occurred the preparation may be rapidly discharged from the site of administration.
A suitable spreading of the formulation on the infected site, if possible followed by an interaction with the mucous layer of the said site, could result in a remarkable increase of the bioavailability of the drug. The said result may be achieved by increasing the duration and the closeness of the contact between medicament and mucous membrane: on these grounds the concept of bioadhesion, and in particular mucoadhesion, has recently gained a remarkable importance in the formulation of systems for the controlled release of drugs for trans-mucosal administration, including, but not exclusively, the systems for vaginal topical administration.
By the term bioadhesion it is meant the creation of an intimate contact, for a prolonged period of time, between a pharmaceutical material and a biological substrate, due to the formation of chemical bonds, to interfacial forces and/or to simple physical interactions between the two surfaces. When the bioadhesive interaction is established between the pharmaceutical material and the mucus which covers most of the tissues, the phenomenon is referred to as mucoadhesion. The advantages obtainable by administering an active ingredient through a bioadhesive pharmaceutical form are manifold, and may be synthesised in the following points:
localisation of the drug in a specific region: this is advantageous in a topical therapy, since the increase in the duration and in the closeness of the contact between pharmaceutical form and tissue improves the bioavailability of the drug;
increase of the in situ residence time: the pharmaceutical form has a prolonged activity, and this allows to reduce the number of daily administrations, thus improving the patient""s compliance;
optimal contact with the absorption surface: this results in a better drug permeation through the tissues, inhibits the degradative enzyme activity on the active ingredient and reduces the mucus secretion;
maintenance of a high concentration gradient between the pharmaceutical form and the absorption site: this allows an optimal release of the drug, in accordance with the known laws describing the passive diffusion.
In the last years a great interest has been shown for the inclusion of bioadhesive polymers in conventional pharmaceutical forms. The so obtained bioadhesive forms mainly consist of polymer materials which are capable of interacting with mucus or with mucins. The features that a bioadhesive polymer should show in order to be pharmaceutically acceptable may be summarised as follows:
absence of toxicity;
ability to form a strong non-covalent bond with the epithelial cells of the mucous surfaces, and to quickly adhere to the moist surfaces;
ability to incorporate the drug readily and in a repeatable way, without exerting any adverse effect on the release thereof.
A number of bioadhesive polymers may be employed, in particular, in vaginal preparations: among the natural hydrogels one may cite starch, collagen, gelatin, some dextrans and also cellulose derivatives, including hydroxypropylmethylcellulose, hydroxypropylcellulose and sodium carboxymethylcellulose. Among the synthetic polymers capable of forming hydrogels only two classes appear to be employed in preparations for vaginal administration: polyethylene oxides (high molecular weight ethylene glycols) and polyacrylic acids.
Among the latter, a particularly advantageous product in view of its bioadhesive properties is polycarbophil (produced by B.F. Goodrich Company of Cleveland, Ohio, under the trade name Noveon(copyright) AA-1). Polycarbophil is an acrylic acid polymer loosely cross-linked with divinyl glycol, in particular with a quantity comprised between 0.5 and 1% by weight of 3,4-dihydroxy-1,5-hexadiene, corresponding to CAS No. 9003-01-04. The particles making out polycarbophil are swellable, but not soluble, in water, and they swell to different extents also in organic solvents, in strong mineral acids and in bases, while remaining insoluble. The water swelling features depend both on pH and on the ionic strength of the solution: the swelling degree increases with increasing pH. The amount of water that the polymer may absorb ranges from 15-35 ml per gram, at low pH values (1-3), to 100 ml per gram, in neutral or basic medium. Polycarbophil is described, together with other polymers of a similar chemical nature, in the U.S. Pat. No. 3,202,577 (R. L. Markus, 1965), where it is proposed for use in the treatment of diarrhoea, in view of its outstanding ability of swelling and absorbing liquids.
Later, it has been found that polycarbophil shows excellent mucoadhesive properties, which have been extensively described in the literature (see, e.g., H. Park and R. Robinson, J. Controlled Release, 2, 1985, 47-57; K. V. R. Rao and P. Buri, Int. J. Pharm., 52, 1989, 265-270). The polymer interaction with mucin is made easier by the fact that the polymer chains undergo swelling in water, and this allows a good degree of interpenetration with the glycoprotein chains of mucus present on the tissues surface.
The mucoadhesive properties mentioned above are actually the core of the European patent publications No. 0 163 696 and No. 0 501 523, in the name of Columbia Laboratories Inc., concerning the use of a class of polymer products, including polycarbophil as the preferred example, as bioadhesives for the production of sustained release pharmaceutical products. In the said documents (the second one of which is a divisional application of the first one) the bioadhesive polymeric product is proposed for use in admixture with pharmaceutical or cosmetic active ingredients, but it has also been proposed, by the same research group, to use polycarbophil alone, for the treatment of various ophthalmic, vaginal and buccal affections, which are characterised by a feeling of excessive dryness of the mucous membranes. In this connection, a product for vaginal rehydration containing polycarbophil has recently been placed on the market, under the trade name Replens(copyright) Said product is said to be able to adhere to the mucosa, while gradually releasing, for about 72 hours, its water content (S. H. Leung and J. R. Robinson, Polym. News, 15, 1990, 333-342).
The European patent No. 0 497 956 discloses sustained release formulations similar to the foregoing ones, but based on the calcium salt of polycarbophil, wherein the active ingredient to be delivered is incorporated in the polymeric matrix formed by calcium polycarbophil through dissolution or dispersion of the active ingredient in the matrix. As an alternative, a hydrogel matrix of calcium polycarbophil may be formed, by adding water to the formulation. The interaction of the polymeric matrix with the active ingredient results in an intimate mixture, through which the active ingredient slowly diffuses and from which it is said to be released in a controlled way.
On the basis of the above known art, it appears that the features of polycarbophil could be advantageously exploited for the production of mucoadhesive mixtures with azole antifungal and/or antiprotozoal drugs for transmucosal administration, in particular for vaginal topical use. With the object of obtaining sustained release bioadhesive products wherein the adhesion of the drug to the mucous membrane to be treated is even higher, thus resulting in a further increase of the above-mentioned advantages brought about by the use of a bioadhesive excipient, the present invention proposes to realise a true complexation between polycarbophil and the azole active ingredient, in its base form. The foregoing results in a new chemical entity wherein the drug is tightly bound to the bioadhesive agent, rather than in a physical mixture between drug and mucoadhesive carrier.
The foregoing is made possible by the chemical nature of the chosen bioadhesive polymer, having reactive carboxyl groups, and of the azole active ingredients, which, when not salified, are of a basic nature. When contacted with each other in suitable reaction conditions, the compounds form complexes which not only benefit from the bioadhesive properties of polycarbophil, but also show a release of the active ingredient extremely prolonged in time and characterised by a uniform rate. In practice, the resulting formulations are capable of: a) adhering to the mucosa as a result of the action of the polymer component, and b) releasing the azole derivative in situ very slowly and with a constant rate.
The administration of azole-polycarbophil complexes shows, when compared with the administration of the corresponding free base or of a salt thereof (e.g., the nitrate), all of the advantages already mentioned with reference to the bioadhesive systems. But also in comparison with the administration of a simple physical mixture of polycarbophil and active ingredient, as it will be clear further on, superior characteristics are obtained as concerns the duration and the uniformity of the delivery, in addition to, obviously, a more intimate and durable contact between the active ingredient and the mucosal surface. The increase of the in situ residence time, together with the type of release of the drug from the complex, result in a prolonged action, thus affording a reduction of the number of daily administrations and an improvement of the patients"" compliance. In addition, the closeness of the contact between the complex and the mucous membrane may allow a higher amount and rate of permeation of the drug through the tissues, while reducing the degradative enzymatic activity on the active ingredient.
Therefore, the present invention specifically provides a mucoadhesive antimicrobial complex of polycarbophil, i.e. a cross-linked polyacrylic acid with bioadhesive properties, and an azole derivative with antifungal or antiprotozoal activity, in its basic form.
In particular, the said azole derivative may be an imidazole derivative, chosen from the group consisting of: econazole, clotrimazole, metronidazole, tioconazole, fenticonazole, isoconazole, ketoconazole, sulconazole, bifonazole, omoconazole, azanidazole, butoconazole and oxiconazole. Particularly preferred for use in the complexes of the invention are econazole, clotrimazole, omoconazole and metronidazole, the first three having antifungal activity, and the fourth one having anti-trichomonas activity.
As an alternative, the azole derivative may be a triazole derivative, such as fluconazole, terconazole and itraconazole. Said compounds show the same antifungal spectrum and the same mechanism of action as antifungal imidazole derivatives, but some of them, differently from imidazoles, may also be administered systemically. In all cases, owing to their chemical nature, the complexation mechanism of triazoles with polycarbophil is similar to that of imidazoles.
The mucoadhesive antimicrobial complexes according to the invention may be obtained, in general, by dissolving each of the two starting products in a common solvent or mixture of solvents, or in two different solvents compatible with each other, then joining together the two solutions in relative amounts such as to contain the same number of equivalents of the starting products, and subsequently evaporating the solvent. Preferably, the solid product obtained from the evaporation is dried, pulverised and sieved. The amount of polycarbophil required is previously calculated by measuring the neutralisation equivalent thereof by potentiometric titration. In the experimentation carried out in the frame of the present invention, the said value turned out to be equal to about 7 meq/g.
According to some preferred embodiments of the invention, the econazole-polycarbophil, clotrimazole-polycarbophil, omoconazole-polycarbophil and metronidazole-polycarbophil complexes are obtained each by preparing two solutions in methanol, one containing the drug in its basic form and the other containing the polymer, the relative amounts of drug and polymer to be dissolved having been calculated in such a way as to obtain in the two solutions an equal number of equivalents of reactant. For polycarbophil the neutralisation equivalent has been evaluated by potentiometric titration carried out with 0.01 N NaOH on 100 mg of polymer, and the result obtained, as pointed out before, is about 7 meq/g. The methanol solutions are mixed together and the resulting solution is placed in an evaporator at 40xc2x0 C. The solid product so obtained is subsequently dried under vacuum at 50xc2x0 C., then pulverised and sieved.
The bioadhesive complexes according to the invention can be used for the production of sustained release antifungal and/or antiprotozoal pharmaceutical products, by incorporating them into suitable formulations together with pharmaceutically acceptable vehicles and excipients. In order to further increase the bioadhesivity of the product, in addition to the complex as such an excess amount of non-complexed polycarbophil may be present. Said excess amount may be of use for adjusting the viscosity and the consistency of the product.
The compositions containing the compounds according to the invention, with a suitable choice of the excipients, may be in any one of the known pharmaceutical forms used for products to be administered by the transmucosal route. For the production of antifungal and/or antiprotozoal medicaments for vaginal administration the gel form is particularly preferred. In the said form the complex according to the invention, if desired together with an excess of polycarbophil, and with other conventional formulation ingredients such as, e.g., preservatives and thickening agents, are formulated in a gel of propylene glycol and/or polyethylene glycol.
By way of example only, some gel compositions containing the complexes of the invention, suitable for vaginal topic administration, are described below.